I dont know bout horse power but i have smoother idle after doing the swap over. Also on my fofo i am running 93 octane with a tune. When dataloging i noticed my air fuel leaned out a bit more in higher rpm which i was looking for because i was at 11.8 af @ 5900, with ar103 @ .047 gap im now 11.4 @ 5900. It really depends on what your looking for. Ar103 dont last as long as motorcraft platinum. In my OPINION its worth it.

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You didn't lean it out.. Going from 11.8 down to 11.4 you actually richened the air fuel mixture.